Electrolytic cell



A. H. W. MEN 223mm@ ELECTROLYTI C CELL Filed March 9, 1938 Patentedl Jan. 28, 1941 UNITED STATES ELECTROLYTIC CELL Adriaan Hendrik Willem Atcn,

Hilversum,

Netherlands, assigner to American Enka Corporation, Enka, N. C., a corporation of Dela-l Ware Application March 9, 1938, Serial No. 104,966

2 Claims.

This invention relates to an electrolytic cell that is particularly useful in recovering metals and acids from aqueous solutions ci their salts. In particular, this invention is directed `to an e electrolytic cell for electrolyzing .aqueous solutions of alkali metal salts to recover the alkali metal hydroxide and acid therefrom.

Prior to this invention, many types of mercury cathode cells lhave been proposed for the lu purpose of decomposing alkali metal salts and recovering the alkali metals therefrom, but the lack of sufciently large `cathode surfaces, the failure of the mercury in these surf-aces to be agitated so as to present continuously fresh surl faces to the solution in the cell, gas formation at the cathode, collecting of the gas below the diaphragm, the necessity of a large volume of mercury, excessive current drop in the cell due to excessive distance between the anode and fthe '-30 cathode, and numerous other diilculties `which the present device also eliminates have `prevented .these cells from being entirely satisfactory.

The .present device is similar in some respects to prior devices, for example, a mercury cathode cell and a diaphragm to separate the anode and cathode solutions are utilized. The arrangement of the present cell is such, however, that the cathode constantly 'presents large areas of fresh 3o mercury -to the solution and the anode is quite close to the cathode and parallel to a plane through .the centers of the [troughs holding the mercury. Substantially even spacing of the anode and cathode is made possible by providing narrow troughs and by using an anode of suitable shape. Furthermore, the diaphragm is so arranged that it aids in the elimination of the gas formed `on the cathode instead of collecting the gas. Numerous other structural details of im the present device which contribute to make it more satisfactory and which are a part of this invention will be apparent from .the following detailed description of the preferred form of this device as shown in the appended drawing.

a5 Figure l is a side sectional view of the device and Figure 2 is a fragmentary sectional view of this device taken along the line 2--2 of Figure 1.

As illustrated, the cell consists of a body mem- 50 ber II, which may be cast or stamped or other- -wlse fabricated from iron or other metal or from glass, hard rubber, wood, or any other desired non-metallic material. When this body member is made of a material that conducts electd -trlcity, such as a. metal, it has been found necat the bottom of this tank or cell a series of weirs I3 which divide the bottom of the tank into a plurality of iiat pans or troughs I4. These lo troughs I4 are arranged so as to be progressively lower from one side of the bottom of the vessel toward the other side so that mercury placed in the highest trough and caused to overflow,

`will overflow into the next lower trough and 1,5

this action will be continuous until the mercury has passed through each of the pans and reached the lowest. Appropriate means are provided to ins-ure continuous passage of the mercury from one trough to the next so that .the cathode sur- 2O face is always spread over the area dened by all of the troughs. For example, a small slot may be present alternatingly near the far and the near end of each subsequent trough in the `di rection of flow of the mercury. An inlet I5 is 25 provided for the mercury, which inlet opens into the highest pan and an outlet IE is also provided for removing the mercury amalgam from the lowest pan.

Above the mercury cathode arrangement, .the body member II is formed so as to receive and support a diaphragm Il, which diaphragm extends completely across the cell and separates the portion of the cell adjacent the cathode from the rest of the cell. An anode I8 is placed above 35 the diaphragm so as to be separatedirom the cathode by the diaphragm.

rihe diaphragm I1 is held by the body member I I in a position which is inclined to the horizontal so that the hydrogen given off at the cath- 4o ode passes upward along the under surface of the diaphragm and out of the cell. The incoming salt solution enters through an opening I9 in the wall of `the body member II, this opening is made suiiiciently large to allow the hydrogen, coming 01T from the mercury, to escape, and is situated just below the diaphragm. The diaphragm is preferably of porous ebonite, but might be of acid-resistant asbestos iiber, a mat of glass fiber held together by an acid-resistant binder, or a ceramic material such as corundum or porous tile.

In addition to being supported by the body member II at the side walls, the diaphragm is preferably also supported by the top edges of the weirs I3 by resting thereon. In order to prevent the mercury in the cathode from coming in contact with the diaphragm, the weirs are constructed as shown in Figure 2 with raised portions 20 which support the diaphragm and lower portion 2I over which the mercury passes into the next lower pan. 'I'hese raised portions are shaped so as to collect as little hydrogen as possible and thereby assist in the elimination of the hydrogen.

In the form of the device shown in the drawing, the anode I8 which is preferably made of perforated sheet lead or alloy thereof is situated above the diaphragm. The current of liquid which flows from the cathode to the anode shows a tendency to carry the diaphragm in upward direction. In order to keep a space between the diaphragm and the anode the latter is provided with protruding ridges which prevent the diaphragm from coming into contact with the Whole surface of the anode.

The top of the cell is open to the air so that any oxygen formed at the anode may pass through the perforations thereof, bubble to the top of the liquid in the cell, and escape or, if desired, be collected. An outlet 22 is provided in the wall of the cell above the anode through which the acidic anode liquid may be discharged.

In operation, a solution of sodium sulphate or similar salt of a reactive metal enters the cell through the opening I9, passes downward along the diaphragm, and runs through the diaphragm into the upper portion of the cell Where it reaches the anode. As it does so, itis electrolyzed and reduced at the mercury vcathode to form an amalgam; at the anode sulphuric acid is formed with evolution of oxygen. The acid liquid is discharged through the opening 22 and the amalgam drawn off through the outlet I6. The metal so recovered may then be removed from the amalgam in any of the usual ways. The mercury thus recovered after removal of said metal is recirculated through the system. Current may be supplied to the anode and the mercury cathode in the usual way, as by the connections 23 and 24, respectively.

The conditions under which the present invention is practiced may be varied; but by way of example, it has been determined that a neutral solution of sodium sulphate at a temperature of to 10 C. above its saturation point will give an anode liquor of 10% to 15% sulphuric acid containing approximately 13% of sodium sulphate. Hence, the device allows a current-output of 90-97%, depending on the acidity required in the anode-liquor and a. bath tension of 5.5-7 volts depending on the currentdensity. Under the aforementioned conditions the electrodes are separated an average distance of less than two inches, for example 0.7 of one inch. The most eiective current density is from 100 to 250 amperes per square foot.

The amalgam passes oil' at outlet I6 to be converted into an alkali metal hydroxide.

What I claim is:

1. In an electrolytic cell for recovering sodium and sulphuric acid from sodium sulphate, the combination of a series of troughs .containing mercury arrangedl to provide a cascade type of mercury cathode, a diaphragm positioned above the cathode and supported on the edges of the troughs of the cathode in a position generally parallel to the cathode in the direction of its inclination, an anode positioned above the diaphragm and supported thereon and also generally parallel to the cathode in the direction of its inclination, an inlet to the cathode compartment to supply sodium sulphate solution exclusively to that compartment, and an outlet from the anode compartment to remove sulphuric acid from that compartment.

2. In an electrolytic cell for recovering sodium and sulphuric acid from sodium sulphate, the combination of a series of troughs containing mercury arranged to provide a cascade type of mercury cathode, a diaphragm positioned above the cathode and supported on 'the edges of the troughs of the cathode in a position generally parallel to the cathode in the direction of its inclination, a foraminous anode positioned above the diaphragm and also generally parallel to the cathode in the direction of its inclination, an inlet to the cathode compartment to supply sodium sulphate solution exclusively to that compartment, and an outlet from the anode compartment to remove sulphuric acid from that compartment. y

ADRIAA'N H. W. ATEN. 

